Influence of Single Dye Molecules on Temperature and Time Dependent Optical Properties of CdSe/ZnS Quantum Dots: Ensemble and Single Nanoassembly Detection

Abstract

Optical spectroscopy on ensembles and single CdSe/ZnS semiconductor quantum dots (QDs) demonstrates a competition of trap and near band edge photoluminescence (PL). This competition can be markedly influenced by a few surface attached pyridyl functionalized dye molecules (porphyrins or perylene diimides) forming nanoassemblies with well defined geometries. Temperature variation and related changes in absorption and emission reveal sharp changes of the ligand shell structure in a narrow temperature range for organic (TOPO and amine) surfactants (phase transition). The effects on QD PL at this transition become considerably pronounced upon attachment of only a few dye molecules to QD surface. Moreover, under ambient conditions amine capped QDs are photodegraded in the course of time. This process is enhanced by attached dye molecules both on the ensemble and single particle/dye level. This investigation elaborates the importance of (switchable) surface states for the characterization of the PL of QDs. © 2012 Elsevier B.V. All rights reserved.